Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 35 kV with the use of transformers.
Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment or household appliances.
Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops.
The transition from transmission to distribution happens in a power substation, which has the following functions:
(1): Circuit breakers and switches enable the substation to be disconnected from the transmission grid or for distribution lines to be disconnected.
(2): Transformers step down transmission voltages, 35 kV or more, down to primary distribution voltages. These are medium voltage circuits, usually 600-35,000 V.
(3): From the transformer, power goes to the busbar that can split the distribution power off in multiple directions. The bus distributes power to distribution lines, which fan out to customers.
Urban distribution can be done underground or overhead. Rural distribution is mostly above ground with utility poles, and suburban distribution is a mix. Closer to the customer, a distribution transformer steps the primary distribution power down to a low-voltage secondary circuit, usually 120/240 V in the US for residential customers. The power comes to the customer via a service drop and an electricity meter. The final circuit in an urban system may be less than 50 feet (15 m), but may be over 300 feet (91 m) feet for a rural customer.
Electricity is delivered at a frequency of either 50 or 60 Hz, depending on the region. It is delivered to domestic customers as single-phase electric power. In some countries as in Europe a three-phase supply may be made available for larger properties. Seen with an oscilloscope, the domestic power supply in North America would look like a sine wave, oscillating between −170 volts and 170 volts, giving an effective voltage of 120 volts RMS. Three-phase power is more efficient in terms of power delivered per cable used, and is more suited to running large electric motors. Some large European appliances may be powered by three-phase power, such as electric stoves and clothes dryers.
A ground connection is normally provided for the customer's system as well as for the equipment owned by the utility. The purpose of connecting the customer's system to ground is to limit the voltage that may develop if high voltage conductors fall down onto lower-voltage conductors which are usually mounted lower to the ground, or if a failure occurs within a distribution transformer. Earthing systems can be TT, TN-S, TN-C-S or TN-C.
When a new conductor is introduced into the electrical distribution system, whether it be transmission, sub transmission or distribution, there is a need to run the wires from structure to structure. The structures can be wood poles, metal poles, lattice towers or fiberglass poles. Most often on main distribution lines, the structure will have four (4) conductors on each pole and sometimes double circuits that could be eight (8) or more conductors. The wires or conductor might run one to four (1-4) miles in town or about forty (40) poles per mile. Each conductor needs a roller to install In town distribution poles have an average spacing of about 132 feet. Line workers install rollers on top of a crossarm or utility arm or hang under an insulator to pull in rope that pulls in the new conductor. The term roller as used herein is used to define blocks with single rollers (such as those that have the appearance of a pulley as well as the inventor's SAR which has a series of rollers as opposed to a single pulley). When there are existing energized conductors on the crossarm or utility arm, line workers have to move the conductors while they are energized to fiberglass temp arms that attach to existing crossarm or utility arms. The reason for this step is to make room to install the rollers to the crossarm or utility arm to pull in the conductor, without having to de-energize the lines and thus cutting power to the end user(s).
The rollers that are used today are typically aluminum construction, which is a conductive material. When the line workers are installing, they are very close to energized existing conductors. There have been many cases in the US where the line workers are injured due to contact with energized parts in their work zone. If the angle needs to be corrected after stringing operation starts the worker needs to remove the conductor, correct the angle on the roller and then reinstall the conductor in the roller.
Further, the typical prior art rollers for use around energized lines use a single full circle pulley. The pulley provides a support area for a transmission or distribution line that has a small bending radius that can damage the inner core of the conductors with two small of a radius that new age carbon core conductors will break. This causes the line to droop or bow between rollers, and can lead to the breakage of the line. Similarly when line workers utilize a spacer cart the rollers of many spacer carts typically are separate single, full rollers. This again creates too steep of a radius and stress point, potentially leading to conductor line breakage. This is particularly troublesome with newer conductor materials. Lineman cannot install large diameter rollers on top of a cross arm because of tight quarters, energized conductors in reach, and large rollers are not generally designed to mount to utility cross arms.
In light of the foregoing, there is a need for an improved roller that allows for safe installation and helps the overloaded electrical grids in the United States by effectively installing carbon core conductors in the distribution circuits. What is further needed is an improved roller that is preferably at least partially non-conductive, preferably allows for a variety of mounting angles, and is lightweight and ergonomic to facilitate installation and removal.